Dynamic LED spectral strategy enhances lettuce (Lactuca sativa) productivity via periodic activation of light-responsive genes and improved light energy use efficiency

Artificial lighting in plant factories typically adopts a static, continuous spectral regime dominated by red light, with red-to-blue and red-to–far-red ratios generally maintained at approximately 3–6:1, resulting in limited exploration of dynamic light regulation strategies. In this study, blue and far-red light were alternately applied at 30-min intervals, reducing their daily light integrals while increasing the proportion of red light, thereby improving light energy utilization and signal responsiveness. Our results demonstrated that alternating light treatments significantly enhanced lettuce yield, with the optimized red-to-alternating light ratio increasing yield by 20.22% compared with the static control. Even low-intensity alternating light induced marked morphological responses, including stem elongation and leaf expansion, resulting in a 16.64% increase in total leaf area and an increase of 2.11 leaves per plant. These effects were primarily attributable to enhanced far-red–induced signaling; although this reduced chlorophyll content, an increased red light proportion maintained the net photosynthetic rate. These phenotypic changes were consistent with elevated expression levels of light-responsive genes, indicating that the dynamic lighting effectively leverages the signal enhancement mediated by alternating light to optimize light energy utilization. Dynamic transcriptome analysis revealed that light-responsive genes exhibited consistent periodic expression during 1-hour alternating light cycles, with expression magnitude modulated by light dose. Moreover, weighted gene co-expression network analysis identified gene modules that were strongly correlated with phenotypic traits and displayed regular response patterns, suggesting that these genes may be directly involved in the light response process in lettuce. These findings demonstrate that alternating light regimes entrain periodic gene activation and thereby enhance the coordination between light energy supply and signal regulation. The optimized dynamic spectral strategy increases artificial light use efficiency and crop productivity, providing a mechanistically informed framework for lighting optimization in plant factories.